1. Field of the Invention
This invention relates to a secondary air supply control system for internal combustion engines, and more particularly to a system which controls an amount of secondary air to be supplied into the exhaust system of an internal combustion engine in a manner reflecting the temperature of catalysts provided in the exhaust system of the engine.
2. Prior Art
There is conventionally known a system for supplying secondary air into the exhaust system of an internal combustion engine in order to promote oxidation of CO and HC in exhaust gases from the engine and oxidizing and reducing reactions of a catalyst provided in the exhaust system and hence purify exhaust gas components. A system of this kind has been proposed, for example, by Japanese Provisional Patent Publication (Kokai) No. 59-138714, which supplies secondary air in amounts suitable for operating conditions of the engine, into the exhaust system, by means of an air pump which is driven by an electric motor, by controlling the rotational speed of the motor in response to operating conditions of the engine (e.g. engine rotational speed, engine load, and engine coolant temperature).
However, the above conventional system does not contemplate the temperature of the catalyst, so that the catalyst becomes activated with delay after the engine is started, thereby causing a temporary degradation in the exhaust emission characteristics.